Alpha material not see through when overlapped
Ok, the answer was in fact possible in Evee, so ignore the "use Cycles" answers.

Use an emission material with varying strength.
Here I have 0.0, 0.33, 0.66, 0.00 and 1.0 strengths from left to right as you view the planes.

Then use the Compositing in nodes to overlay the rendered image over the background image in the screen mode. This makes has the desired effect of making the 0.00 material transparent to the background but NOT show the objects behind it through the material.

The edges are drawn using the Freestyle tool sets.